Feasibility Study for Performance Prediction of Circumferentially Compound-Stage Model Turbines

A concept for reducing the testing time of turbine-stage families is proposed, and its feasibility is investigated using CFD. A compound stage is used, whose blading around the circumference varies sectorwise, each sector containing a sequence of equal blades that are different from the blades in the neighboring sectors. The example chosen involves three blade types in the stator and rotor, realizing temporarily nine different stage configurations during a rotor revolution. The application of fast-response flow-measuring techniques is required for such configurations because global measurements of mass flow and torque are not relevant. The CFD study in a generic subsonic research turbine stage and the subsequent performance analysis are aimed at showing that the time-dependent short-lived flow fields in the compound stage are representative of flow fields obtained in stages with equivalent but circumferentially uniform bladings. A 2D unsteady Euler solver is used to predict the full annulus time-dependent flow field within the compound- and uniform-stage. The time-average of the unsteady results are fed into loss correlations leading to performance maps for the nine stage configurations in the compound stage. The comparison of the computed compound stage results with the uniform stage suggests that this concept for assessing the performance of subsonic turbine stages is basically feasible. This opens up the prospect for time-resolving fluid flow measuring systems to be successfully applied in such configurations for rapid stage prototyping. (Author)